Automatic telephone system



C. LOB/EAX AUTOMATIC TELEPHONE SYSTEM March 8,1927, LJl

Original Filed March 16, SL92; 4 Sheeis-Sheet 2 fx hum-H?" Zlranc' .EL Umax March "s, 1927. ,1,620,113

C. E` LOMAX AUTOMATIC TELEPHONE SYSTEM Original Filed March 16. 1921 4 Sheets-Sheet rs March 8,1927. JZQB c. E. LOMAX AUTOMATIC TELEPHONE SYSTEM Original Filed March 16. 1923 4 Sheets-Sheet 4 Patented Mar. 8, 1927.

CLARENCE E. LOMAX, OF CHICAGO, ILLINOIS, ASSIGNOR, BY MESNE ASSIGNMENTS, T0

AUTOMATIC ELECTRIC INC., OF CHICAGO, ILLINOIS, A CORPORATION OF DELA- WARE.

AUTOMATIC TELEPHONE SYSTEM.

Application filed 'March 16, 1921, Serial No. 452,840.

T he present invention relates in general to automatic telephone systems, but more particularly to small automatic systems of the type commonly used for giving telephone service in factories, business houses, or other private establishments; and the object of the invention, broadly stated, is to provide a private automatic exchange system embodying new features and novel circuit arrangements for giving effect to these features, whereby a system is produced which is better adapted than others to fill the commercial re quirements of the present time.

The principal object in mind, during the design of the circuits, was to produce a private automatic exchange system which will operate without change in conjunction with either a manual or automatic main exchange. 'The importance of this will be appreciated from the fact that at present a great many manual systems are being replaced by automatic systems, and from the probability that eventually all manual systems will be so replaced. Under, these conditions, operating telephone companies desire to have such new private branch exchange installations as they make from time to time of such a character that they will continue to give service without change during and after the, substitution of th-e automatic equipment in the main exchange.

According to the present invention an operator is employed to complete main to branch exchange connections and a further feature is an improved arrangement for giving night service when the operator is away from her position. A minor feature in this connection is an arrangement whereby certain local lines are denied access to the main exchange trunk lines at ordinary times during the day, while all the local lines are given access to such trunk lines when the night service connections are up.

A further feature is concerned with a well known type of conference calling arrangement, and involves a saving in apparatus over the schemes formerly known to applicant.

Still other features relate to novel means for making a trunk line busy to local switches when it` is taken for use at the main exchange; to an improved means for controlling the disconnect signals in the branch exchange cord circuits; to an improved ar- Renewed J'uly 20, 1925.

rangement for giving the main exchange operator supervision on main to branch eX- change calls; to a novel method of controlling a locking ring down relay over a trunk line so that the same can be unlocked from the distant end; and to new circuit arrangements for supplying talking current to branch exchange subscribers when they are called from the main exchange.

There are still other features not now specifically mentioned but which, together' with the above, will be described fully here-A inafter with reference to the accompanying drawings.

In order to fully illustrate and describe the invention it has been shown in conjunction with a manual main exchange which it is assumed is about to be cut over to auto matic. operation. As stated hereinbefore, the circuits of the invention have been designed to work in conjunction with either a manual or an automatic main exchange and it is understood, therefore, that at the time of the cut over no change is necessary in the apparatus at the private automatic exchange. Prior to the cut over all telephone lines in the manual main exchange are equipped for automatic service by the installation of individual line switches and the usual automatic equipment. Before the out over and while the automatic equipment is being installed the cut olf relays in the subscribers individual line switches are mechanically placed in an operated position so that up to the time of the cut over the exchange will work manually in the usual manner. When the time for the cut over arrives new directories are issued, the subscribers are notified through the medium of local newspapers or any other convenient means, and are advised that in making calls after the set time they will have to operate the calling devices at their telephones. In the exchange the cut off relays on the line switches are restored to their normal condition and the lines leading to the manual equipment are cut, or otherwise disconnected. Thereafter the exchange operates in the usual automatic manner.

Figures 1 to l show a system embodying the invention and should be arranged in order with Figure 1 at the left.

Referring now to the drawings, in Fig. 1 is shown a subscribers telephone A2 having the manual line equipment terminating in jack J1n and the automatic individual line equipment or line switch C2. The jack J10 appears at some A operators position, and there are also the usual multiple acks, either at the A board or at a so called B board, depending on the size of the system. These arrangements are well known and on that account only the answering jack is shown.

The cord circuit O is of a well known type and is used for extending the line of any subscriber to that of another subscriber or to trunk lines leading to other exchanges. The jack J11 is a terminal of such a trunk line extending to a private automatic exchange. The line switch C2 is of the well known rotary type and has access to trunk lines terminating in selector switches simi lar to the one shown at E. The selector E is of the usual Strowger vertical and rotary type and has access to trunk lines terminating in connector switches one of which is shown at H2, Fig. 2.

The connector H2 is of the well known Strowger type and has access to main exchange subscribers lines, one of these being shown at A3, and to trunk lines leading to the private automatic exchange. The bank contacts 385-588, inclusive, represent terminals of such a trunk line which is the same as the one terminating in ack J11 before the operator. This trunk line extends to the private automatic exchange where it terminates in jacks J and J 2, Fig. 3, at the attendant operators position.

At O', Fig. 3, is shown the cord circuit at the attendant operators position in the private automatic exchange. The auxiliary jack J of the trunk is used for night service only. The ack J 3 is the terminal of a trunk line extentfing to an incoming` automatic connector switch which is shown at H, Fig. 4. This connector is of the usual Strowger type having access to local subscribers lines such as that of the substation A. At A, Fig. 4, is shown an automatic substation of the usual type having the rotary line switch C individual thereto. The line switch C in common with a plurality of other line switches has access to trunk lines terminating` in the local connector selector' repeaters, one of these being shown at H', Fig. 4. This switch is of the well known Strowger type having 100 bank contacts arranged in tcn rows or levels. On the first eight levels this connector has access to local subscribers lines as has the connector H. These local lines are, of course, multipled in the usual manner throughout all the connector switches. On the ninth level the connector H has access to ring down trunks going to another manual exchange. Un the tenth level are accessible trunk lines leading to the main exchange. As shown, the bank contacts 370-372, inclusive, represent the terminal of such a trunk line, being the same one as is shown connecting Figs. 2 and 3.

Although the wiring of the banks of the switch H will be readily understood, it will be briefly explained. The bank contacts 370-372, inclusive, are the terminals of the trunk line leading to the public manual exchange, Figs. 1 and 2, and as shown are the multiples of the trunk line shown incoming to Fig. 3. The bank contacts 375-377, inelusive, are the terminals of a trunk line leading to another manual exchange. The conductors leading from the bank contacts 379-381, inclusive, terminate in the night service equipment shown at N, Fig. 3. Bank contacts 384-386, inclusive, are 'the terminals of the conference number in the connector H.

Having briefly described the apparatus in which the invention is involved a detailed description of its operation will now be given. The description will first be given according to the assumption that the main exchange is operating manually, and it will be assumed that the subscriber at substation A2 in the main exchange desires to call the subscriber at substation A (Fig. 4) in the branch exchange.

@alle from the manual maia exchange to the prwae automatic exchange.

`When the receiver is removed at substation A2 a circuit is completed for line relay 409 over the line conductors 401 and 402 in series. Upon energizing, relay 409 at armature 412 lights the line lamp L10 before an operator. This operation signals the operator at whose position the answering jack J10 appears and she will respond to the call by inserting the answering plug of an idle cord circuit, the cord circuit O for example, into the answering jack J1". Vhen the plug is inserted into the jack the cut off-relay 410 is energized, the circuit of the line relay 409 is broken and the line lamp L10 is extinguished. At the same time a circuit is completed over the sleeve of the cord for the answering su pervisory lamp L11 but since the receiver is off the hook at substantion A2 the supervisory relay 420 will at once operate and shunt out the lamp L1 to prevent it from .lighting at the present time. The operator may now throw the listening key K5 in the cord circuit O in order to answer the calling subscriber and ascertain what number he desires. Having found that the desired party is the subscriber at substation A in the distant private automatic exchange the operator will test the jacks associated with the trunk lines extending to such exchange with the tip of the calling plug in the usual manner and she will insert the plug in the first idle jack. Assuming that the trunk line shown in the drawing is the first idle trunk line the calling` plug lm will be inserted into the jack J 11. A circuit is thereby completed for the cut oft relay 426 over the sleeve of 'the cord. The answering supervisory lamp L12 is inincluded in lthis circuit and hence operates. Relay 426, upon energizing, disconnects the normal battery and ground connections from the trunk conductors 428 and 429 at armatures 611 and 610 and at armature 430 completes the circuit of the slow acting relay 427. The latter' relay, upon energizing, opens a point in the circuit of the line lamp L13 associated with the trunk line at armature 433 and at the front contact of this armat-ure prepares a locking circuit for itself and at armature 432 removes one connection 0f ground to lthe cut olf relay. However this latter operation is without function at this time as ground is still connected to the cut oft relay from the back contact of armature 435 of 'the line relay 425. The battery supplied by the operators cord circuit to the trunk conductors 428 and 429 is of opposite polarity to that normally supplied when the trunk line is not in use. The relay 27 in the trunk circuit at lthe private automatic exchange is a high resistance polarized relay, normally energized by the battery on the trunk and consequently it will retract its armature 38 and close its associated contacts whenever battery is removed from the trunk or reversed thereover. It will be seen that by this arrangement should the trunk accidentally go open or be seized by an operator, as in the present case, the relay 27 will retract its armature. In either case, upon deenergizing, relay 27 completes a circuit extending from ground by way of back contact and armature 34, armature 38 and its resting contacts and thence through the winding of the slow acting relay 28 to battery. Upon energizing, this latter relay at armature 40 places ground on release trunk conductor 136 extending to local connector switches such as the connector H thereby making the trunk line busy for any outgoing calls and at armature 39 completes a point. in the talking connection. The main exchange operatoi` will now operate her ringing key KG thereby impressing ringing current upon the trunk. This will serve to operate the ring up relay 25 which energizes, establishes a locking circuit for itself at armature 32, and at armature 3l completes the circuit of the line lamp L. It will be seen that the relay 25 at armature 33 also short circuits the condenser thereby placing its lower winding in bridge of the trunk conductors. However its lower winding is of such high resistance that the supervisory control "relay 421 in the calling operators cord circuit is not energized. lf for any reason the main exchange operator withdraws the plug P11 from the jack J11 before the attendant has answered the cut o relay 426 will deenergize restoring 'the normal battery supply to the trunk conductors. This operation will consequently re.- verse the direction of currei'it iiow in the lower winding of relay 25. ris the magnetic fields produced by the windings of relay 25 now oppose each other this relay will deenergize. It will be understood, of course, that the armatures 32 and 33 are so adjusted that they break away from their front contacts simultaneously, thus any fluttering of the relay armatures is prevented. By the deenergization of relay 25, the line lamp L is effaced and thus all apparatus is returned to normal.

It will now be assumed that the branch exchange operator notices the lighting of the line lamp L. This signal will serve to notify the attendant operator in the private automatic exchange that a connection is desired and she will, therefore, insert the plug of an idle cord circuit, which we will assume is the plug P of the cord circuit O', into the jack J2. By this operation a circuit is completed extending from ground through the winding of relay 50 by way of the sleeve of the plug P, sleeve of the jack J2, and thence Ithrough the winding of relay 26 to battery in multiple with the busy visual 29. Upon energizing, relay 26 opens the locking circuits of the ring up relay 25 at armatures 35 and 36 and at armature 34 opens a point in the circuit of relay 28 but the springs 7l are closed by the plug P being shoved into the jack J2 so this operation has no effect at this time. The locking circuits of the relay 25 now being open this relay will d-eenergize thereby, extinguish-y ing the lamp L. The operation of the busy visual is without function at this time. Relay 50 upon operating, completes a circuit extending from ground by way of front contact and armature 60, spring 77 of key K and its resting contact, armature 71 and its back coni act, and thence through the answering `supervisory lamp L6 to battery. When the plug P is inserted in the jack J2 a bridge is placed across the talking conductors, the circuit of which may be traced from the tip of plug P, spring 7 6 and its resting contact, winding of relay 53, winding of relay 52, back Contact and armature 70, winding of relay 54, resting contact of .spring 75 and the said spring, and thence to the ring of plug P. As battery is now supplied to the trunk from the windings of the repeating coil in the main exchange operators cord circuit, relay 52 cnergizes. Owing to the high rcsistance of relay 52, relays 53 and 54 in the att-endants cord circuit and the supervisory control relay 421 in the calling operatoi."s cord circuit are not operatively 4energized at this time. Relay 52 upon operating. opens a point in the circuit of relay 51. it will be seen that the circuit of relay 51 is broken by the energization of relay 52 before relay 51 has had time to energize and so this relay is not operated at this time. The attendant operator will now throw the listening key K thereby associating her head set with the cord circuit and enabling her to ascertain what number the main exchange operator desires. l/Vhen the key K is thrown the high resistance relay 52 is shunted out and the relays 53, 54, in the attendants cord circuit O are energized While the supervisory control relay 421 in the cord circuit O at the main exchange is also operated. The Ioperation or' relay 421 serves to extinguish the supervisory lamp L12 in the cord-circuit O thereby notifying the main exchange operator that the attendant has answered. Relay 53, upon operating, at armature 67, closes another short circuit around the relay 52 so that even when the key K is restored to normal the supervisory lamp in the main exchange operator-s cord circuit Will remain extinguished until the called subscriber has answered and finally hung up. Relay 54, upon energizing, serves to maintain a point in the circuit of relay 51 open, thus preventing this relay from energizing. When the attendant operator iinds out what number is desired she will insert the plug ly into an idle jack, Which We Will assume is jack J3 extending to the incoming connector switch H, Fig. 4. By this operation a circuit is completed for the line relay 150 of the connector H over a circuit which extends from ground by Way of normally closed springs controlled by relay springs or' the calling device S, key K2, spring 7 9 and its Working contact, sleeve of the plug P, sleeve ot the jack J3, .springs 80, conductor 126 and thence through the Winding of the line relay to battery. The line relay 150 ivill energize over this circuit completing the circuit of the slovi7 acting relay 151, which energizes to prepare the circuit of the switch H :tor operating. It will be noted that the line relay 150 is not connected directly to the sleeve of the jack J3, this provision is made so that there will be no impulse sent to the line relay 15() due to a contact being made between the tip of the plug P and the sleeve of jack J3 While the plug is being inserted into the jack J3. Ground is olf course present on the tip of the plug P, being supplied from the cord circuit in the main exchange. r1`hus no impulses will be sent to the line relay 150 until the operator operates her calling device.

rlhe attendant operator may now operate her calling device S in accordance with the lirst digit of the desired subscribers number thereby producing a corresponding series of interruptions in the above traced circuit of the line relay 15() which deenergizes a plurality of times in response thereto. At each retraction of its armature a circuit is completed extending from ground by Way of armature 170 and its back contact, armature 173 and its front contact, off normal springs 178 and 179, through the winding of the vertical magnet 161 and then through the Winding of the slow acting series relay 152 to battery. The above is the circuit over Which the first vertical impulse is transmitted. Upon the first vertical step of the shaft, the off normal springs are shifted and the remaining impulses to the vertical magnet traverse a different circuit which is the same as the one previously traced except that it includes the oli normal springs 178 and 180, and armature 187 and its front contact, relay 152 being new in an operated position. Magnet 161 operates to raise the Wipers 215-218, inclusive, step by step until they are placed opposite the level of bank contacts in which is located the terminals of the line of the substation A. The slow acting relay 152, Which is energized in series with the vertical magnet, maintains its armature attracted throughout the vertical movement of the switch and at the termination thereof deenergizes and transfers the operating circuit to the rotary magnet 162.

The attendant operator may noiv operate her calling device in accordance with the tinal digit ot the called subscribers number, las before, producing ay series of interruptions in the circuit of the line relay 150 Which deenergizes a plurality of times in response thereto. Upon each deenergization, a circuit is completed extending from ground by Way ot' armature 170 and its back contact, armature 173 and its front contact, od normal springs 178 and 180, armature 187 and its back contact, back contact and armature 196, through the Winding of the slow acting relay 155, armature 209 and its back contact, and through the Winding of the rotary magnet 162 to battery. Magnet 162 operates to rotate the Wipers 215-218, inclusive, into engagement with the set of bank contacts associated with the line of the subscriber at substation A which, We Will assume, are the bank contacts 220-223, inclusive. The slovv acting relay 155 is energized in series With the rotary magnet and operates to connect the test Wiper 217 to the test relay 154. lf the desired subscribers line should be busy at this time a ground potential will be present on the bank contact 222. A circuit may then be traced extending vfrom the said grounded test contact by way ot' the test Wiper 217, armature 201 and its front contact, and through the Winding ot the test relay 154 to battery. Relay 154 encrgizes over this circuit lestablishing a locking circuit for itself at armature and at armature 198 placing the busy tone on the loiver line conductor 127. This tone ivill flow back to the attendant operator and to the calling subscriber and serve to inform them that the desired line is busy. Should the calling subscriber at substation A2 now desire a connection with another subscriber in the branch exchange he will inform the attendant of this fact. The attendant will then operate the release key K2 thereby opening the circuit of the line relay 150 of the connector H. lWhen this relay deenergizes the slow acting release relay 151 deenergizes shortly after, and the connector switch is released in the well known manner. The operator may now by operating her calling device for the digits of desired subscribers number cause the connector H to connect with this line. The operation in this case is identically the same as that just described and will be readily apparent.

However should the calling subscriber at substation A2 replace his receiver the supervisory signal in the cord circuit O would be operated and the operator would withdraw the plugs P10 and P11 of the cord circuit O from the jacks, thereby causing l the lamp L5 in the attendants cord to become lighted. The attendant operator, upon receiving the disconnect signal, withdraws the plugs P and P', thereby releasing all the apparatus. These operations will be described fully hereinafter.

It will now be assumed that the line of the subscriber at substation A was idle when connection thereto was attempted. Under these circumstances, there will be no ground potential on the test contact 222 and no circuit will be completed for the test relay 154. Then, following the deenergization of the slow acting relay 155, a circuit is completed extending from ground on release trunk conductor 185, by way of `normally closed springs controlled by relay 152, armature 195 and its back contact, through the lower winding of the switching relay 156, back contact and armature 201` test wiper 217, test contact 222, through the winding of the switching relay 225 of the line switch C', and thence through the winding of the stepping magnet 227 to battery. The relays 156 and 225 operate over this circuit. However, due to a mechanical interlocking device controlled by the armature of the line relay 226 which has not been energized, the switching relay 225 only attracts its armatures enough to disconnect the line of substation A from its normal battery and ground connections in the line switch C. Relay 156, upon energizing, establishes a locking circuit. for itself at armature 207, places ground on the test wiper 217 at armature 208, and at armatures 205 and 210 completes the ringing circuit.

Having completed the desired connection the attendant operator may now restore her listening key K. This operation opens the first shunt around the high resistance relay 52 but as the relay 53 is energized the relay 52 is maintained short circuited by the armature 67. In this manner the supervisory signal in the cord circuit O of the main eX- change operator is not again operated.

Returning now to the operation of the connector H, ringing current is then intermittently applied to the line of the substation A until an answer is obtained. W'hen this occurs a circuit for direct current is completed over the called subscribers line for the ring cut off relay 153. Upon energizing', this latter relay establishes a locking circuit for itself at armature 191 and at armatures 190 and 192 cuts 011' the ring and at the front contacts of these armatures finally completes the talking connection.

When the ring cut off relay 153 in the connector H energizes, a direct metallic circuit extends from the repeating coil in the cord circuit O to substation A. This circuit it will be seen, includes the relays 54 and 55 in the cord circuit O. Relay 55, upon operating, opens the bridge extending through relays 52, 53, and 54 at armature 70. Relay 53 restores, but since relay 54 is in series with the lower talking strand, it remains operated to maintain the circuit of relay 51 open after relay 53 restores. Relay 53, in restoring, removes the shunt from relay 52 to permit this relay to operate later on. Relay 55 also at armature 71 lopens the circuit of the supervisory lamp L. This latter operation serves to notify the attendant that the called subscriber has answered. The conversation may be carried on over the heavy talking conductors between the main exchange subscriber at substation A2 and the subscriber at substation A', battery being supplied to the subscriber at substation A through the right hand windings of the repeating coil in the cord circuit O of the main exchange operator and to the main exchange subscriber from the left hand windings of the same repeating coil.

`When the conversation is terminated, both subscribers will replace their receivers upon their switchhooks. Upon the receiver being replaced at the calling substation A2, the supervisory control relay 420 is deenergized and the lamp L11 is lighted. /Vhen the receiver is replaced at the called substation A the supervisory relays 54 and 55 in the cord circuit O deenergize. Relay 55, upon retracting its armatures, closes the circuit of the supervisory lamp LG and places the relays 52, 53 and 54 again across a bridge ot the cord circuit. Owing to the high resistance ot this bridge, the relay 52 not having its winding shunted at this time, relays 54 and the supervisory control relay 421 in the cord circuit O are deenergized. By the deenergization of relay 421 the lamp L12 is lighted. The relay 52 again operates and at its armature 64 opens a point in the circuit of relay 51 before slow release relay 54 has deenergized. The operator in the main exchange, upon noting the lighting or" the lamps L11 and L12, will withdraw the answering and calling plugs of the cord circuit O from the jacks J1@ and J 11 thereby restoring the apparatus in the main ex change to normal. Immediately upon the plug Pllbeing' withdrawn from the jack Jn, the cut oil' relay 426 deenergizes, the circuit of the slow acting relay 427 is opened, and the normal battery connections are replaced 'on the trunk conductors 428 and 429. lVhen this reversal takes place the relay 52 in the cord circuit 0 momentarily deenergizes and completes a circuit extending from ground by way of front contact and armature 60, springs 77, back contact and armature 66, armature 64 and its baclr contact, armature 72 and its back contact, normally closed springs controlled by armature 61, and thence through upper winding of the relay 51 to battery. The relay 51, energizes over this circuit and, upon operating, establishes a loc-king circuit for itself at armature 61, at armature 62 closes a low resistance bridge across the trunk conductors, and at armature 63 lights the calling disconnect signal L5. rl`he low resistance bridge placed across the trunk conductors by the energization or' the relay 5l serves to energize the line relay 425 of the trunk circuit in the main exchange. A locking circuit is then completed for the slow acting relay 427 at armature 435. It will be understood that the relay 427 being slow acting does not retract its armatures before the line relay 425 has had time to energize. Relays 425 and 427 now being energized the circuit of the cut 'off relay 426 is opened at armatures 432 and 435 and a busy potential is placed on the sleeve of the jack J 11 associated with this trunk line, at armatures 434 and 431. Now should the main exchange operator try to connect with this trunk line she will receive a busy test. In this manner the trunk line is prevented from being seized until the branch exchange operator has finally taken down the connection in the branch exchange.

Upon noting the signals L5 and LG, the attendant operator will know that the conversation is terminated and she will withdraw the plugs of the cord circuit O from their associated jacks.

By this last operation the connector H and all the apparatus in the branch exchange is released. As soon as the plug P is withdrawn from the jack J2 the relays 26 and 28 are deen'ergized, the busy potential is thus removed :trom the multipled release trunk conductor in the outgoing level of the local connector switches and the polarized and ring up relay 25 and 27, respectively, are replaced across the trunk conductors.

In the main exchange the lin-e relay 425 de* energizes due to the low resistance bridge through relay 51 having been broken, thus opening the locking circuit oi the slow acting relay427, removing the'busy test from the jack J 11, and replacing the ground connection of the cut ott relay. In the above manner all apparatus is returned to normal.

The connector H is also arranged so that it may be used for rotary service, that is, it can select and connect with an idle line in a group of lines or should all lines in a group be busy, notify the calling subscriber of this fact. lts operation in this case is well known and similar to that ot the connector H2, Fig. 2, the operation o'l" which will be described fully hereinafter.

It will be noted that the connector' H which has access to the same lines as the connector H is not arranged for rotary service. The reason for this is that incoming calls are often important and it' certain numbers are called it is o'lten the practice to enable the connector H to connect with any idle one of a number of telephones. lnside calls are not usually so important and any subscriber in the branch exchange will know these other numbers anyway and he can call them separately.

Nif/lat service calls from the manual main efr/'change 250 the private automatic cchange.

rllhe above is the normal operation of the system when the attendant operator is on duty. During the night, however, there will probably be no operator in charge and so provision must be made7 for night calls. This is secured by means of the night cord O2. The operator, upon going olf duty, will. place the plugs P2 and P3 ot the night cord O2 into the jacks J and J4, respectively. By this operation the night circuits are completed. The operation of the system under these conditions will now be described.

For this purpose it will again be assumed that the subscriber at substation A2 desires to call the private automatic exchange. lVhen the receiver is removed at the calling substation the line relay 409 is energized and the line lamp lighted. As bcore, the operator at whose position the lamp appears will insert the answering plug or' an idle cord circuit O into the jack J and operate her listening key. Upon being informed that the branch exchange is desired the operator will test the jacks of the trunk lines extending to the private automatic exchange and insert the calling plug ot the cord circuit O into the jack or the first idle trunk line, causing the operation of the polarized relay 27 in a manner hereinbefore described. Upon operating, this relay completes the circuit of the slow acting relay 28 which energizes to apply a busy potential to the release trunk of the outgoing trunk line which is accessible to the local switches. It will be seen that by the insertion of the plug P2 into the jack J the springs 15 are opened and the ring up relay 25 is therefore removed from across the trunk conductors. lVhen the operator presses her ringing key KG ringing current will flow over the trunk conductors t28 and 129, jack J', cord circuit O2, jack J4, and thence through the bells 98, 99 and 100. A plurality of these bells are located at convenient places throughout the factory and serve to notify the watchman or whoever is in charge at night that a call is being made. A special number is provided for this service arrangement and the watchman will of course be aware of this number. Upon hearing the night bells ring he will go to the nearest telephone, which we will assume is the substation A, remove his receiver, and operate his calling device for the number assigned to night service.

W hen the receiver is removed at substation A a circuit is completed for the line relay 260 of the individual line switch C over the line conductors 250 and 251 in series. Upon energizing, the line relay at armature 266 completes a circuit which includes the switching relay 261 and the stepping` magnet 262 in series and at armature 265 connects the test wiper 277 to the above circuit at a point midway between the switching relay and the said stepping magnet. The operation of the rotary line switch C now depends upon whether or not the trunk line with which the wipers 275-278, inclusive, are associated is or is not busy. If busy, a ground potential will be present on the test contact engaged by test wiper 277, the switching relay 261 will be short circuited, and the stepping magnet being supplied with direct ground by way of the said test wiper will operate as a buzzer to advance the switch step by step in search of an idle trunk line. lt will be assumed in the present case that the trunk line leading from bank contacts 280-283, inclusive, is'idle and it will be further assumed that this trunk is selected for use by the line switch C. Vihen this occurs the switching relay 261. being no longer short circuited, will energize in series with the said stepping magnet. t may be stated at this time that the switching relay is of very high resistance so as to prevent the operation of the stepping magnet. Upon energizing, the switching relay 261 disconnects the line conductors 250 and 251 from the winding of the line relay and from ground, respectively, and extends them by way of armatures 268 and 271 and their front contacts, wipers 275 and 278, bank contacts 280 and 283, and through the upper and lower windings of the line relay 300 of the local connector selector repeater H. The line relay 300 will energize over the line circuit and at armature 315 complete the circuit of the slow acting relay 301 which energizes preparing the operating circuits of the switch H at armature 319, and at armature 318 places ground on the release trunk conductor 320 thereby establishing aholding circuit which extends by way of bank contact 232, test wiper 277, armature 270 and its front contact, through the winding of the switching relay 261 and the winding of the stepping magnet 262 to battery. A branch of this circuit also extends by way of the private normal conductor 252 to multiply connected test contacts in the banks of local connector switches such as the switch H and simila' switches which have access to the line of the substation A. This multiple has not been shown for the reason that it is well known and would unduly complicate the drawings. It will be understood of course, that the above holding circuit is completed before the deenergization of the line relay 260.

The watchman will now operate the calling device at substation A in accordance with the first digit assigned t-o the night service number thus producing a series of interruptions in the circuit of relay 300 which deenergizes in response thereto. t each retraction of its armature 315 a circuit is completed extending from ground by way of armature 315 and its back contact, armature 319 and its front contact, olf normal springs 353 and 354, winding of the slow acting series relay 302, and the winding of the vertical magnet 311 to battery. rihe above is the circuit over which the first vertical magnet impulse is sent. Upon the first vertical step of the shaft, the off normal springs are shifted and the impulses to the vertical magnet travel over a new path which includes the springs 353 and 355 and arlnature 321i and its front contact. The vertical magnet 311 operates to raise the switch wipers 360-362, inclusive` step by step until they are placed opposite the level of bank contacts in which is situated the night servico number. The slow acting relay 302, which energized in series with the vertical magnt-at, maintains its armature attracted throughout the vertical operation of the switch and at the termination of the vertical movement deenergizes transferring theloperating circuit to the rotary n'iagnet 312.

rlhe watchman may now operate his calling device in accordance with the last digit of the night service number. As before, the line relay 300 responds to the interruptions in its line circuit and at e ch retraction of its armature completes a circuit extending as follows: ground by way of armature 315 and its back Contact, armature 319 and its front contact, off normal springs 353 and 355, armature 321i and its back contact, normally closed springs controlled by relay 306,

tlf)

lill' lllfi armature 351 and its back contact, and, thence through the winding ot the rotary magnet 312 to battery. Magnet 312 oper'- ates to rotate the switch wipers into .engagement with the contact set associated with the night service number, which we will assume, is the bank contacts 379-381, inclusive. The springs 338 are cam springs adapted to be operated when the switch wipers are rotated into engagement with Ieither the conference 'or night service number. A circuit is now completed ext-ending from ground through the lower winding of relay 304, cam springs 338, and through the lower winding of the ring cut ott' rclay 305 to battery. Relay 304, upon operating, places the impedance 303 across the talking conductors and relay 305 pr-epares a point in the talking connection. The slow acting relay 307 is energized in multiple with the rotary magnet and operates to connect the test wiper l361 to the test relay 306. The night number will of course be idle at this time as there is no necessity of it being used except by the watchman. Upon the .deenergization of the slow acting relay 307, shortly after the termination ot' the rotary movement of the switch, a circuit is completed extending from ground on release trunk conductor 320 by way of armature 340 and its back contact, lower winding of the switching relay 308, back contact and armature 346, normally closed springs controlled by the switching relay 308, test wiper 361, test contact 380, conductor 129, and thence through winding ot the relay 91 to battery. The switching relay 308 will energize over this circuit and upon operating, establishes a locking circuit for itself at armature 349 and at armatures 348 and completes the talking connection. Relay 91 will be lenergized over the previously traced circuit and upon operating, opens the circuit of the bells 98, 99, and 100 at armature 92 and at armature 93 completes a circuit extending from ground by way ot front contact and armature 93, sleeve ot jack J4, sleeve of plug P3, sleeve of plug P2, sleeve ot. jack Je', release trunk conductor 136 to multiply connected test contacts in the banks ot local connector selector repeaters, whereby the outgoing trunk line is prevented from being seized by any unrestricted branch exchange subscriber even if the operator at the main .exchange should pull down the connection before the watchman hangs up his receiver. By the etl'accment of the super visory signal L12 in the calling main exchange operators cord circuit the operator will be informed that the night watchman has answered. Conversation may now be carried on between the calling subscriber at substation A2 and the watchman at substaton A. lhen it is terminated the nightwatchman by hanging up the receiver at substation A releases the connector H and again lights the supervisory lamp L12 and upon the operator withdrawing the plug ot' her cord circuit from the jack Jn all the apparatus is restored to its normal position.

Calls from the attendant at the private antomatz'e exchange to the main exchange.

The attendant operator at the private automatic exchange may sometimes find it necessary to call the main exchange operator. In order to do this she will insert the plug of an idle cord circuit, which we will assume is the plug P of the cord circuit O', into the jack of an idle trunk line extending to the main exchange and operate her calling out key K. When the plug P is inserted into the jack J2 a circuit is completed over the sleeve of the cord for the relays 50 and 26 and the busy visual 29. Relay 26, upon operating, opens the circuit ot' the polarized relay 27 which relay retracts its armature into engagement with its associated contact either when the circuit ot 27 is opened, or when the battery is reversed. By the insertion of the plug P into the jack J2 the springs 71 .are closed and when relay 27 retracts its armature a circuit is completed extending from ground by way ot' springs 71, armature 38 and its associated contact and thence through the winding of relay 28 to battery. Relay 28, upon energizing, places ground on the multiplied release trunk conductor 136 in the banks of selector connector repeaters thus rendering the trunk line busy in the usual manner. Relay 28 at armature 39 also prepares a point in the operating or signalling circuit of the lamp associated with this trunk line in the main exchanges.

It will be noted that the relay 28 is not energized and consequently the armature 39 is not attracted until the plug is fully inserted in the jack. This arrangement prevents any false operation ot the line signal associated with the trunk line in the main exchange, should the operator plug in with her calling out key K thrown. Relay 50, upon energizing, operates in the same manner as before, and completes the circuit ot the supervsiory lamp LG. The relays 52 and are now in bridge ot the trunk conductors and relay 52 energizes thereby opening the circuit ot relay 51. By the operation of the calling out key K these relays are deenergized but the relay 51 is not energized for the reason that a point in its circuit is broken at springs 77 of key K. Another result of the operation of the key K is that a circuit is completed extending from ground through spring 81 and its working contact, and through the winding of relay 80 to battery. Relay 80, upon energizing, prepares thc signalling circuit for the main exchange operator. This circuit extends over the following path: from ground by way of back contact and armature 610, trunk conductor 429, ring ot the jack J2, ring of the plug P, spring oit' key K and its working contact.l right hand windings ot the repeating coil, armature and its front contact, springs of the calling device S, springs ot key K2, spring 82 and its working contact, tip ot plug P, tip ot jack J 2, trunk conductor 423, armature G11 and its back Contact, and through the winding ot the line relay 425 to battery. Relay 425 is energized over this circuit and completes a circuit at armature (512 for the line lamp L13. lNhen the main exchange operator notes the lighting of the lamp L13 she will place the answering plug ol an idle cord circuit into the jack J 11 thereby completing the circuit for the cut ol'l' relay 426 over the sleeve of her cord. By throwing the listening key K5 in the cord circuit- O which it will be assumed is the cord circuit used to answer this call, the main exchange operator will be able to communicate with the attendant operator in the private automatic exchange and ascertain what she desires. After inding the number of the desired main exchange subscriber the operator will test lthe desired line to see it itis idle. lt such be the case by then inserting the plug P11 into the jack of the desired local line which we will assume is that of the substa tion A2, a circuit is completed for cut oli relay 410 over the sleeve ot the plug and also for the answering supervisory lamp L12. lf'lilhen the ringing key KG is operated ringing currentis imposed on the line from the ringing generator in the usual manner. lllhen the called subscriber answers the circuit is completed over the line tor the supervisory control relay 421 which, upon operating, short circuits the lamp L12 thereby notifying the operator that the call is being answered. Conversation may now take place between the attendant operator in the branch exchange and the called subscriber in the main exchange, battery being supplied to the called subscriber from the windings of the repeating coil in the cord circuit O and to the attendant operator -from the local battery associated with her headset. `When the conversation is terminated the called subscriber by replacing his receiver will light the associated supervisory lamp L12, and upon the attendant operator withdrawing the plug P 'from the jack J 2 the lamp L11 is operated. The main exchange operator will now withdraw the answering and calling plugs from the jacks J 11 and J1@ thereby restoring the apparatus to normal. l 00.723 from the private automatic exchange subscribers to the mamie-Z main exchange.

rl`he private automatic exchange is also provided with what is known as a restricted service. ln this arrangement only certain subscribers are allowed to make outgoing calls to the main exchange. This is accomplished by placing an extra wiper on all the line switches and those subscribers who are entitled to outgoing service have this extra wiper connected to ground. The manner in which the system operates in this case will now be described.

For this purpose we will assume that the subscriber at substation A desires to make an outgoing call and it willbe assumed urther that he is a non-restricted subscriber. Vihen the receiver is removed at substation A a circuit is completed tor the line relay 260 ot the line switch C. The line switch C will then operate as before described to extend its associated line to an idle connector switch which we will assume is the switch H. The line relay 300 ot' the connector H is energized over the. line circuit and upon operating, completes a circuit ot the slow acting release relay 301. As before, the latter relay, upon energizing, prepares the circuits of the connector H for operation at armature 319 and at armature 318 establishes a holding circuit for the line switch C, a branch of this circuit also extending to multiply connected test contacts in the banks of the connector switches whereby the said line is protected :trom intrusion in the usual manner.

As the trunk lines leading to the main exchange terminate in the tenth level, the subscriber will operate his calling device in accordance with the digit O. Then interruptions are thereby produced in the line circuit of relay 300 which operates to control the operation of the vertical magnet 311. Magnet 311 operates to raise the switch wipers 5360-362, inclusive` opposite the tenth level of bank contacts. The springs 3550-333 ar-e shat't springs adapted to be actuated when the switch wipers are raised opposite the tenth level or" bank contacts. This may be accomplished by any suitable cam arrangement. To continue, when the switch wipers are raised to the tent-h level the springs 330 and 332 are forced into engage ment with their workingcontacts. By the operation of the spring 330 a circuit is cornpleted extending trom ground through the lower winding otl relay 304 by way o't shatt controlled springs 330 and 331 and through the lower winding of the ring cut oi'i relay 305 to battery. Upon energizing, relay 305 establishes a locking circuit for itself at armature 336 and at armatures 335 and 337 prepares a point in the talking circuit. Relay 304, upon operating places the impedance coil 303 across the talking conductors of the switch H. The relay 302, which is energized in s-eries with the vertical magnet, maintains its armature attracted for a short interval after the termination ot the vertical movement ot' the switch. As soon as the springs 332 and 323 close,- a circuit is completed. from ground on discriminating trunk 321 by way of shaft controlled springs 332 and 333, springs 326 and 325, armature 323 and its front contact, back contact and armature 343, and through the winding of the test relay 306 to battery. Upon energizing, relay 306 establishes a locking circuit for its-elf at armature 340 and at armature 341 prepares the rotary magnet circuit. Upon the deenergization of the slow acting relay 302, a circuit is completed extending from ground on discriminating trunk 321 by way of shaft controlled springs 332 and 333, springs 326 and 325, armature 323 and its back contact, armature 341 and its front contact, armature 351 and its back contact, and through the winding of the rotary magnet 312 to battery. Magnet 312 operates to rotate the switch wipers into cugagement with the first set of contacts in the tenth level and to break the locking circuit of the test relay 306 which deenergizes opening the circuit of the rotary magnet which deenergizes also. The slow acting relay 307 is energized in multiple with the rotary magnet and operates as before, to connect the test wiper 361 to the test relay 306. The further operation of the switch depends upon whether or not the trunk line, with which the switch wipers are in engagement, is busy or idle. If busy, there will be a ground potential present on the test contact engaged by test wiper 361. A circuit may then be traced extending from the said grounded test contact by way of the test wiper 361, normally closed springs controlled by relay 308, armature 346 and its front contact, back contact and armature 343, and through the winding of the test relay 306 to battery. Relay 306 will energize over this circuit to again complet-e the rotary magnet circuit. This alternate operation of the test relay 306 and the rotary magnet 312 will continue until an idle trunk is found which, we will assume, is the trunk line associated with the bank contacts 370- 372, inclusive. Vhen this occurs there will be no ground potential present on the test contact 371 engaged by the test wiper 361. No circuit will therefore be completed for the test relay 306. Then, following the decnergization of the slow acting relay 307, a circuit is completed extending from ground on the release trunk conductor 320 by way of armature 340 and its back contact, lower winding of the switching relay 308, back contact and armature 346, normally closed springs controlled by armature 350, test wiper 361, test contact 371, conductor 136, armature 40 and its back contact, and through the winding of relay 26 and the busy visual 29 to battery. The conductors 135-137, inclusive, shown in Fig. 4, extend to Fig. 3 where they are indicated by the They have not same reference numerals.

been shown extending from nu@ figure t0 the other in the drawings for the reason that their inclusion would complicate the circuits.

It will be seen that relays 308 and 26 are operated over the above traced circuit, relay 26, upon operating, opens the circuits of the polarized relay 27 at armature 36. The circuit of the polarized relay 27 being opened now at armature 36, armature 38 will be retracted into engagement with its associated contacts, but this operation will have no function at this time. The busy visual, upon operating, serves to notify the attendant operator that this trunk line is in use. The switching relay 308 upon energizing, establishes a locking circuit for itself at armature 349 and at armatures 348 and 352 completes a signalling circuit whereby the line signal L13 in front of the main exchange operator is lighted. The circuit by which this is accomplished may be traced from battery through the winding of relay 425, by way of back contact and armature 611, trunk conductor 428, conductor 135, (Fig. 3), conductor 135 (Fig. 4), bank contact 372, wiper 362, front contact and armature 352, armature 337 and its front contact, front contact and armature 316, lower winding of the impedance coil 303, armature 335 and its front contact, front contact and armature 334, upper winding of the impedance coil 303, back contact and armature 345, front contact and armature 335, armature 348 and its front contact, wiper 360, bank contact 370, conductor 137 (Fig. 4), conductor 137 (Fig. 3), trunk conductor 429, and thence by Way of armature 610 and its back contact to ground. Relay 425 energizes over this circuit and at armature 435 completes the circuit of the line lamp L13. This signal will serve to notify the operator that a branch exchange subscriber desires to make a call and she will insert the plug of an idle cord circuit into the jack J 11, thereby extinguishing the lamp L13 and upon throwing her listening key placing herself in communication with the calling subscriber. After ascertaining what number the calling subscriber wishes, the connection may be completed in accordance with well known manual practice as described hereinbefore. lhen the conversation is terminated the calling subscriber at substation A by replacing his receiver upon the switchhook initiates the release of the switch H in the usual manner.

Restricted service.

As before mentioned, the private automatic exchange is provided with what is known as restricted services whereby certain subscribers only are allowed to make outgoing calls to the main exchange and to the second manual exchange, that is they are restricted from using certain levels of the local switches, namely, the ninth and tenth,

in which are terminated trunk lines extending to these two exchanges. The manner in which restricted service subscribers are discriminated against will now be explained. For this purpose it will be assumed that the subscriber at substation A is restricted service subscriber. In this case armature 269 in the individual line switch C will not be connected to ground.

lVhen the receiver is removed at substation A. the line switch C operates to extend the line of the subscriber at substation A to an idle connector selector repeater which, we will assume, is the switch H. Upon the calling device at substation A being operated for the digit 0 the line relay 300 responds to the interruptions in its line circuit to control the operation ef the vertical magnet 311. Magnet 311 operates to raise the switch wipers step by step until they are placed opposite the tenth level. When this occurs the shaft controlled springs 330 and 332 are forced into engagement with their working contacts. As before, the slow acting relay 302 is energized in series with the vertical magnet and maintains its armature attracted for a short interval after the termination of t-he vertical movement of the switch. In the present case there will be no ground present on the discriminating trunk 321. By the operation of the shaft controlled springs 330 and 331 a circuit is completed extending from ground by way of the lower winding of relay 304, shaft controlled springs 330 and 331, and through the lower winding of the ring cut off relay 305 to battery. Relays 304 and 305 operate over this circuit. Relay 305 upon energizing, establishes a locking circuit for itself at armature 336 and at armatures 335 and 337 prepares a point in the repeating circuits. Relay 304 upon attracting its armature places the impedance 303 in bridge of the talking concluetors. hen the springs 332 and 333 close a circuit is completed extending from ground on release trunk conductor 320 through the resistance 304', shaft controlled springs 332 and 333, springs 326 and 325, armature 323 and its front contact, back contact and armature 343, and through the winding of the test relay 306 to battery. Relay 306 will energize in series with the upper winding of relay 304.

Upon operating, relay 306 establishes a locking circuit for itself at armature 340 and at armature 341 prepares the rotary magnet circuit. Following the deenergization of the slow acting relay 302 a short intei-val after the impulses to the vertical magnet have ceased a circuit may be traced extending from ground on release trunk cenductor 320 by way of upper winding of relay 304, shaft controlled springs 332 and 333, springs 326 and 325, armature 323 and its back contact, armature 341 and its front con- .lL-Mu tact, armature 351 and its back contact, and through the winding of the rotary magnet 312 to battery. However, the rotary magnet will not operate in series with the resistance 304', as it does not receive enough current to energize. It will new be seen that a busy tone is placed on the lower talking conductor at armature 339, by the operation of the test relay 306. In this manner the subscriber at substation A is informed that he is not allowed outgoing service and upon replacing his receiver he will release the cennector selector repeater Il as before described.

It will be seen that by this discriminating feature only certain telephones are allowed to make out-going calls. At night this arrangement might be objectionable for the reason that the watchman may not be near a telephone that has outgoing service when he desires to make a call to the main eX- change and hence unless special provision is made he would be unable to do se. In the present case, however, provision has been made to take care of this difficulty. The manner in which this is accomplished will now be described.

Nag/tt calls to #ze maf/a exchange 'by the watchman at the private automaten exchange.

In order to make outgoing call from any telephone the night watchman will be instructed to call the night service number that is ordinarily used for answering night calls. It will be assumed that the watchman is at substation A and that he proceeds to make a night call in this manner. TWhen the receiver is removed at substation A individual line switch C operates as before described to select an idle connector selector repeater H.

lVhen the calling device at substation A is operated for the first digit of the night service number a series of interruptions are produced in the circuit of the line relay 300. Relay 300 operating in response to these impulses controls the operation of the vertical magnet 311 in stepping the wipers opposite the level of bank contacts in which is located the night service number.

The watchman may now operate his calling device for the final digit of the night service number'. Now the line relay controls the operation of the rotary magnet 312 in rotating the wipers into engagement with the bank contacts assigned to night service which, we will assume, are the bank contacts 379-381, inclusive. All the above operations take place in a manner hereinbefore described. The slow acting relay 307 is energized in multiple with the rotary magnet and operates to connect the test wiper 361 to the test relay 306.

It will be assumed that the night number is idle when connection thereto is attempted. Under these circumstances there will be no ground present on the test Contact 330 and no circuit will be completed for the test relay 300. Then, following the dcenergization ot the slow acting relay 307, a circuit may be traced extending from ground on release trunk conductor 320, by way of armature 340 and its back contact, lower winding of the switching relay 303, back contact and armature 340, normally closed springs controlled by armature 350, test wiper 361, bank contact 380, conductor 129, and then through the winding ot the relay 91 to battery. Relays 01 and 308 operate over this circuit. Relay 91, upon energizing, removes the bells from across the trunk at armature 92 and at armature 93 completes a circuit extending over the following path: ground by way of armature 03 and its front contact, sleeve ot the jack J4, sleeve of the plug P3, sleeve of the plug l, sleeve ot the jack J', where the circuit divides, one path extending to the multipled release trunk conductor 136 in the outgoing level et the banks of connector selector repeaters, and the other path extending by way of armature 40 and its back contact, through the winding of relay 26, and the winding ot the busy visual 29 to battery. Relay 26 operates to remove the ring up relay 25 from across the bridge of the trunk conductors 428 and 429 and also to open the circuit of the polarized relay 27. The latter relay in'unediately retracts its armature but as ground is removed from its armature 33 by the operation of relay 20 this operation has no function at this time. The busy visual of course operates in the usual manner but as there is no attendant operator at the position this operation is also without function. A circuit may now be traced eX- tending from ground by way of back contact and armature 010, trunk conductor 429, ring ot the jack J, ring ot the plug P2, ring ot plug P3, ring of jack J1, conductor 130, bank contact 331, wiper 362, front contact and armature 352, armature 337 and its front contact, front contact of armature 316 and the said armature, lower winding of the impedance coil 303, armature 335 and its front Contact, front contact and armature 334, upper winding of the impedance coil 303, back contact and armature 345. front contact and armature 335', armature 343 and its Atrent contact, wiper 300, bank contact 379, conductor 123, tip ot' jack J4, tip of plug l, tip o't the plug 1, tip ot the jack J, trunk conductor 428, armature 011 and its back contact, and through the winding oi the line relay 425 to battery. Relay 425, upon energizing, completes a circuit for the line lamp L13 before the operator in the manual exchange. When the main exchange operator notices the lighting of the lamp L13 she will insert the answering end of an idle cord circuit, such as the cord circuit O, into the jack .111, thereby completing a circuit for the cut oil' relay 426 over the sleeve of her cord. Relay 426, upon operating, removes normal battery and ground connections from the trunk connectors 428 and 429. It will be noticed that this circuit includes the ans swering supervisory lamp L11, but as the circuit is completed at the same time for the supervisory control relay 420 which immediately operates to short circuit the lamp L11, the lamp will not remain lighted. 1n order to ascertain what number the branch eX- change subscriber desires the operator will throw her listening key K5. The subsequent operations by which the connection is eX- tended to vthe desired local station and iinally released will all take place in the usual manner.

Zocal calls between, subscribers of the private automatico' exchange.

The manner in which a local call is completed will now be described. F or this purpose it will be assumed that the subscriber at substation A desires to call the subscriber at substation A. i

lVhen the receiver is removed at the calling substation the line switch C operates in the usual manner to extend the line of its associated subscriber to an idle connector switch which, we will assume, is the connector H. `When the calling device is operated for the first digit of the desired number the line relay 300 in responding to the interruptions in its line circuit controls the operation of the vertical magnet 311, which operates to raise the switch wipers 360-3627 inclusive, step by step until they are placed opposite the level ot bank contacts in which is located the desired subscribers line.

`When the impulse sender at the calling substation is operated in accordance with the nal digit in the number of the desired subscriber at substation A a series of interruptions is again produced in the line circuit of the line relay 300. As before, relay 300 responds to these interruptions and at each retraction of its armature sends an impulse or current to the rotary magnet 312 in multiple with the slow acting relay 307. Magnet 312 operates to rotate the switch wipers into engagement with the set of contacts associated with the line ot the subscriber at substation A which we will assume is the set comprising bank contacts 339-391 inclusive. The slow acting relay 30T upon operating connects the test wiper to the test relay 300. It the line of the subscriber at substation A is busy at this time there will be a ground potential present on test contact 390 and a circuit will be completed for the test relay 306 which will energize and transmit the busy signal to the calling subscriber as described hereinbefore,

However, it will be assumed in the present case that the line of the subscriber at substation A was idle at this time. Then, following the deenergization of the slow acting relay 307, a circuit is completed extending from ground on release trunk conductor 320 by way of armature 340 and its back contact, lower winding of the switching relay 308, back contact and armature 346, normally closed springs controlled by relay 308, test wiper 361, test contact 390, through the winding of the switching relay 225 of the line switch C and the winding of the stepping magnet 227 to battery. Relays 308 and 225 operate over this circuit. Relay 225 only attracts its armature enough to disconnect the line of the substation A from its normal battery and ground connections. Relay 308, upon operating, locks itself energized at armature 349 and at armatures 348 and 352 completes the ringing circuit of the subscriber at substation A. Ringing current is then intermittently projected over the line of the called substation until an answer is obtained.

`When this occurs the circuit is completed for the ring cut 0H relay 305 which energizes and establishes a locking circuit for itself at armature 336 and at armatures 335 and 337 opens the ringing circuit and at the front contacts of these armatures finally completes the talking connection. Conversation may now take place between the calling and called subscriber over the heavy talking conductors, battery being supplied to the calling subscriber from the windings of the line relay 300 and battery being supplied to the called subscriber from the windings of the back bridge relay 303. lVhen the conversation is terminated the release of the connector H will take place upon the calling subscriber at substation A replacing his receiver upon the switchhook.

UaZZs from- Hze private automat/0 @archange to the second manual cmctaf/zge.

As before stated, the connector selector repeater H also has access to ring down trunks going to the second manual exchange. The operation of the switch when this exchange is called will now be briefly described. For this purpose it will be assumed that the subscriber at substation A who is a non-restricted subscriber desires to call the second manual exchange. As the trunk lines leading to the second manual exchange terminate in the ninth level, the digit 9 will be called.

When the calling device is operated for the digit 9, the wipers of the selector connector repeater H will be raised to the ninth level. By this operation the shaft controlled springs 332 and 333 are closed.. As before, slow acting relay 302 1s energized 1n series with the vertical magnet and, the shaft springs 332 and 333 being now' closed, a circuit is completed at armature 323 for the test relay 306. Upon the termination of the vertical movement of the switch, relay 302 deenergizes and a circuit is completed for the rotary magnet 312 in multiple with the slow acting relay 307. The trunk selecting operation will now take place in the same manner as hereinbefore described. The test relay 306 is energized each time the wipers engage a busy trunk line and operates to complete the rotary magnet circuit. Vhen an idle trunk is found which, we will assume, is the trunk line terminating in bank contacts 37 5-377, inclusive, there will be no circuit for the test relay 306. A circuit is then effective following the deenergization of relay 307 extending from ground on release trunk conductor 320 by way of armature 340 and its back contact, through the lower winding of the switching relay 308 back contact and armature 346, normally closed springs controlled by relay 308, test wiper 361, test contact 376, and through resistance R to battery. Relay 308 will operate over this circuit to establish a locking circuit for itself at armature 349 and at armatures 348 and 352 completing the ringing circuit.

The desired connection has now been established, ringing current is automatically projected out on the trunk line the same as in the case of a called local line and the ring down drop at the manual switchboard is operated in the usual manner. When the operator plugs in to answer the call the ring cut off relay 305 is operated. This relay operates to open the ringing circuit and tol comn plete the talking connection. The connec` tion to the desired station in this manual exchange may be completed by the operator through the medium of any suitable means which need not be explained herein.

Conference calls.

The private automatic exchange is also provided with a feature that is known as conference calling. This ,is an arrangement to enable three or more subscribers lines to be telephonically connected together at the same time. The most common way of accomplishing this result is to have the subscriber that is setting upa conference call each party individually and inform him that a. conference is to be held. At the predetermined time all the parties desired in the conference will call a special number. In order to enable the parties to connect with the same number the. test contacts in the banks of the various local connector switches are not multipled but instead the test contact associated with the conference number in each switch is connected to the locking winding of the switching relay.

In order to explain the operation of this conference feature it will be assumed that the subscriber at substation A desires to set up a conference. He will first remove his receiver and in the usual manner call the various parties he desires in the conference, after which he will connect with the conference number. The local connections set up by the subscriber at substation A will be substantially the same as the ones hereinbefore described and so it will only be necessary to explain the operation when the subscriber at substation A connects with the conference number.

Then the receiver is removed at the calling substation the individual line switch C operates in the usual manner to extend the calling subscribers line into connection with an idle local connector selector repeater. It will be assumed that the connector selector repeater H was idle at this time and is selected for use by the line switch C.

The line relay 300 of the switch H is energized over the calling subscribers line loop and in the usual manner closes the circuit of the slow acting release relay 301 which operates as before described to complete a holding circuit for the line switch C and to prepare the operating circuits of the connector H.

lVhen the calling device at substation A is operated for the first digit the line relay 300 responds to the interruptions in its line circuit and controls the operation of the vertical magnet 311 in stepping the switch wipers opposite the level of bank contacts in which is located the bank contacts associated with the conference number. The slow acting relay 302 is energized in series with the vertical magnet and maintains its armature attracted throughout the vertical movement of the switch and at the termination thereof deenergizes and transfers the operating circuit to the rotary magnet 312.

The subscriber at substation A may now operate his calling device in accordance with the last digit of the conference number. As before, the line relay retracts its armature a plurality of times in response to the interruptions in its line circuit each time sending an impulse of current to the rotary inagnet 312 in multiple with the slow acting relay 307. Magnet 312 operates to rotate the switch wipers into engagement with the bank contacts associated with the conference number which, we will assume, are the bank contacts 334-386, inclusive. The slow acting relay 307 energizes and at its armature 346 connects the test wiper 361 to thel test relay 306. However, as the test contacts of the conference number are not multipled there will be no ground present on the testcontact 385 and no circuit will be completed for the test relay 306. When the switch wipers are rotated into engagement with the bank contact associated with the conference number a rotary cam on the switch shaft forces the cam spring 338 into engagement with its working contact. A circuit is now completed extending from ground through the lower winding of the relay 304, spring` 338 and its working contact, and thence through the lower winding of the ring cut off relay 305 to battery. Relays 304 and 305 are energized over this circuit. Relay 304 operates to bridge the impedance coil 303 directly across the talking conductors and relay 305 operates to prepare a point in the talking connection. Then, following` the deenergization of the slow acting relay 307, a circuit is completed for the switching ree lay 308 extending over the following path: from ground on release trunk conductor 320, by way of armature 340 and its back contact, lower winding of switching` relay 308, back contact and armature 346, normally closed springs controlled by armature 350, test wiper 361, test contact 385, and thence through the upper winding of the switchingrelay 308 to battery. Relay 308 is energized over this circuit and upon operating, establishes a locking circuit for itself at armature 349 and at armatures 348 and 352 finally completes the talking connection. It will be seen that the calling subscriber at substation A is now in communication with all the other subscribers in the conference by way of the multipled line conductors of the conference number, talking battery being supplied to each one from the windings of the line relay of the associated connector switch. lVhen the conference is terminated the subscribers included therein, by replacing their receivers upon the switchhooks.r will initiate the release of their associated line and connector switches in the usual manner. In the operation above described it will be seen that the test contact of the conference number in each connector switch is connected to the locking winding of the switching relay in the associated connector switch. It will be apparent that by this con struction it is unnecessary to connect a battery feed coil to each of these contacts as was necessary heretofore and consequently a material saving is effected in the cost of installation.

@alla from 71e automatic maia @archange to thc pre/vate automatic exchange.

is removed at the calling substation A2 a circuit is completed for the line relay 451 of the individual line-switch C2 over the lll!) line conductors 401 and 402 in series. The line switch C2 will new operate in the usual manner to select an idle trunk line extending to a first selector switch, which it will be assumed, is the selector E. `When this occurs the switching relay 450 energizes and extends the calling subscribers line to the line relay 470 of the selected selector E.

The line relay 470 energizes over the calling subscribers line loop and at its armature 480 completes a circuit of the slow aeting release relay 471. Upon energizing, the latter relay at armature 483 prepares the operating circuits of the selector E and at armature 482 places lground on release trunk conductor 484 thereby establishing a holding circuit which extends by way of test contact 465, test wiper 461, armature 454, through the winding of the switching relay 450 and thence through the winding of the stepping magnet 452 to' battery. This holding circuit serves to maintain the switching relay in an operated position throughout the connections. A branch of the holding circuit also extends by way of the private normal conductor 458 to multiply connected test contacts in the banks of connector switches which have access to the line of substation A2 whereby the said line is protected from intrusion in the well known manner.

The calling subscriber may now operate his calling device in accordance with the first digit of his desired number. By this operation a series of interruptions is produced in the circuit of the line relay 470 which retracts its armature a corresponding number of times in response thereto. At each retraction of its arma-ture 480 a circuit is completed extending from ground by way of back contact and armature 491, armature 480 and its back contact, armature 488 and its front contact, winding of the slow acting series relay 472, and through the winding of the vertical magnet 477 to battery. Magnet 477 operates to raise the switch wipers 494-496, inclusive, step by .step until they are placed opposite the desired level of bank contacts. The slow acting relay 472 is energized in series with the vertical magnet and upon the first v-ertical step of the shaft the olf normal springs 478 close and a circuit is completed extending from ground on release trunk conductor 484 by way of armature 485 and its front contact, oft' normal springs 478 and thence through the winding of the interrupter relay 473 to battery. Upon energizing, the latter relay at armature 487 establishes a locking circuit for itself, and at armature 488 prepares the rotary magnet circuit. An instant after the termination of the vertical movement of the selector E the slow acting relay 472 is deenergized and a circuit is completed extending from ground on release trunk conductor 484 by way of armature 485 and its back contact, armature 488 and its front contact, and through the winding of the rotary magnet 476 to battery. Magnet 476 operates to rotate the switch wipers into engagement with the terminals of the iirst trunk lin-e in this level and at armature 498 opens the locking circuit of the interrupter relay 478. The latter relay then deenergizes opening the eircuit of the rotary magnet which deenergizes also. The operation of the selector E now depends upon whether the trunk lin-e with which the switch wipers 494-496, inclusive, are associated is busy or idle. lf busy, there will be a ground potential present on the test Contact engaged by test wiper 495. A circuit is then completed extending from the said grounded test Contact by way of armature 49() and its back contact, back contact and armature 493, off normal springs 478, and through the winding of the interrupter relay 473 to battery. Relay 478 energizes over this circuit and operates in the same manner as before to establish a locking circuit for itself and to complete the rotary magnet circuit. As before, magnet 476 operates to rotate th-e switch. wipers another step into engagement with the next trunk in the selected level and at the same time to break the locking circuit of the interrupter relay 473 which relay deenergizes breaking the rotary magnet circuit which deenergizes also. lllhe alternate operation of the interrupter relay 47 and the rotary magnet 476 will continue until an idle trunk is found, which, it will be assumed, is the trunk lin-e comprising conductors 50G-502 and terminating in bank contacts 4974499, inclusive. When this occurs there will be no ground potential present on the test contact 498 engaged by the test wiper 495. The switching relay 474 which has heretofore been short circuited by ground on various test contacts will energize over a circuit extending from ground en release trunk con* ductor 484, through the winding of the switching relay 474, back contact and armature 498, ellI normal. springs 478, and through the winding of the interrupter relay 473 to battery. It may loe stated at this point that the switching relay 474 is of con'iparatively high resistance so as to prevent the energization of the interrupter relay 473 in series with it. Upon energizing, the switching relay 474 disconnects the incoming line cenductors from the windings of the line relay and extends them by way of armatures 489 and 492, wipers 494 and 496, bank contacts 497 and 499., trunk conductors 500 and 502, normally closed springs controlled by relay 510, upper and lower windings of the line relay 511 of the connector H2 to battery.

The line relay 511 is energized over the calling subscribers line loop and closes the circuit of the slow acting release relay 512 at armature 535. Upon energizing, the latter relay at armature 538 prepares the circuits of the connector H2 for operation and at armature 537 places ground on release trunk conductor 501 thereby establishing a holding circuit which extends by way of test contact 498, test wiper 495, armature 490 and its front contact, at which point it di Vides one circuit extending through the winding of the switching relay 474 of the selector E, the other extending back to switching relay 450 of the line switch C. This holding circuit serves to maintain the line switch C2 and selector E in an operated position.

rlhe calling subscriber may now operate his calling device in accordance with the next digit of the subscribers number at substation A. A series of interruptions are thus produced in the circuit of the line relay 511 which retracts its armature a plurality of times in response thereto. At each retraction of its armature a circuit is completed extending from ground by way of armature 535 and its back contact, armature 538 and its front contact, off normal springs 541 and 546, winding of the vertical magnet 519, and through the winding of the slow acting series relay 514 to battery. The above is the circuit over which the first vertical impulse is transmitted. Upon the first ver` tical step of the shaft, the olf normal springs are shifted and the remaining impulses tov the vertical magnet traverse a new circuit which is the same as the one previously traced except that it includes the off normal springs 541 and 542 and armature 549 and its front Contact (relay 514 being now in an operated position). The vertical magnet 519 operates to raise the switch wipers 580-583, inclusive, step by step until they are placed opposite the level of bank contacts in which is located trunk lines going to the private automatic exchange. The slow acting relay 514 is energized in series with the vertical magnet and maintains its armatures attracted throughout the vertical movement of the switch and at the termination thereof deenergizes and transfers the operating circuit to the rotary magnet 521.

The calling subscriber may now call the next digit of his desired number. As before, a series of interruptions is produced in the line circuit of the relay 511 which retracts its armature a corresponding number of times. At each retiaction of its armature an impulse of current is sent to the rotary magnet 521 over the following path: ground by way of armature 535 and its back contact, armature 538 and its front contact, off normal springs 541 and 542, armature 549 and its back contact, back contact and armature 559, winding of the slow acting series relay 517, armature 573 and its back contact, and thence through the windingA of the rotary magnet 521 to batter Magnet 521 operates to rotate the switci wipers 580-583, inelusive, into engagement with the first trunk line leading` to the private automatic exchange. The slow acting relay 517 is energized in series with the rotary magnet and operates to connect test wiper 581 to the test relay 516. The operation of the switch now depends upon whether or not the trunk line with which the wipers are associated is busy or idle.

lVhere there are a number of trunk lines extending to a private automatic branch exchange the connector H2 must be able to connect with the tirst idle trunk line ex tending to suoli an exchange or if all trunks are busy to return the busy signal to the calling subscriber. In order to arrange the connector H2 to give this class of service two test wipers are provided. In order to enable the switch to rotate over busy lines the test contacts engaged by the test wipers must be tied together and those of the last trunk line in the group are left open.

Returning now to the operationV of the connector H2 when engagement is made with the `first trunk line leading to the private automatic exchange. Supposing this trunk line to be busy a ground potential will be present on test contacts engaged by the test wipers 581 and 582. A circuit is then completed extending from the grounded test contact engaged by wiper 581 by way of the said test wiper, armature 564 and its front contact, armature 574 and its back contact, and through the winding of the test relay 516 to battery. Relay 516 operates over this circuit establishing a locking circuit for itself at armature 558 and preparing the circuit for interrupter relay 513. Vhen the slow acting series relay 517 is deenergized a circuit is completed from the grounded test contact engaged by the test wiper 582, by way of the said test wiper, armature 563 and its back contact, back contact and armature 570, back contact and armature 567, armature 56() and its front contact, through the winding of the interrupter relay 513, and thence through the winding of the slow acting relay 514 to battery. Upon energizing, relay 513 at armature 546 establishes a locking circuit for itself, and at armature 545 completes the rotary magnet circuit. Magnet 521 operates to rotate the switch wipers into engagement with the second trunk line leading` to the private automatic exchange and to break the locking circuit of the interrupter relay 513. The latter relay deenergizes breaking the circuit of the rotary magnet which deenergizes also. The slow acting relay 514 which is energized in series with the stepping relay operates to maintain the test wiper 581 in connection with the test relay 516. If this trunk line should also be busy, 

